|Al Jazeera's Yvonne Ndege reports from the Liberian capital, Monrovia [Reuters]
Nine Liberian opposition parties, including President Ellen Johnson Sirleaf's two main challengers, have rejected results announced so far for this week's presidential election and said party members would withdraw from the rest of the counting process.
The head of Liberia's election commission rejected the allegations of fraud on Saturday, saying the vote was credible.
"It doesn't pose any credibility problems," National Election Commission Chairman James Fromayah told journalists. "All the parties participated in the elections. The counting was done and both the local population and the international observers that came acclaimed the process to be free, fair and transparent."
According to the latest results, Sirleaf was leading with 44.6 per cent of the votes, ahead of Winston Tubman of the CDC party, slightly up on 31.4 per cent of some 950,000 valid votes counted.
Despite the lead, Sirleaf remains short of the outright majority required for a first-round win.
"We declare the results being reported by the National Election Commission as fraud and are consequently declared null and void by all parties signatory to this release," an opposition statement said.
The statement, released before the latest batch of results were announced, had been signed by nine parties representing eight of the country's 14 presidential candidates, including Tubman and third-placed former rebel Prince Johnson.
'No evidence of fraud'
An official from the Carter Center, an election watchdog, said they were aware of the statement but they had not seen any evidence of fraud.
Some 1.8 million Liberians registered to vote. A run-off will take place in early November if no candidate secures more than 50 per cent.
The opposition party statement also called on party representatives following counting to withdraw from the process and said that they would hold a peaceful rally on Sunday.
There was no immediate reaction in the streets of Monrovia but in an apparent sign of tensions surrounding the poll, a spokesman for Sirleaf's Unity Party said one of their offices had been set ablaze overnight.
"We believe it was politically motivated," Bushema Keita told Reuters.
Voting on Tuesday passed generally peacefully and no observer missions have flagged any serious irregularities in the process so far.
The election was Liberia's first locally organised poll since an on-and-off 1989-2003 conflict, and if smooth could pave the way for billions of dollars in mining and oil investment.
Liberia, which suffered two devastating back-to-back civil wars, has now closed its borders with Ivory Coast, Guinea and Sierra Leone, a security source told AFP news agency.